Transcriptome profiling of sheep granulosa cells and oocytes during early follicular development obtained by Laser Capture Microdissection

<p>Abstract</p> <p>Background</p> <p>Successful achievement of early folliculogenesis is crucial for female reproductive function. The process is finely regulated by cell-cell interactions and by the coordinated expression of genes in both the oocyte and in granulosa cells. Despite many studies, little is known about the cell-specific gene expression driving early folliculogenesis. The very small size of these follicles and the mixture of types of follicles within the developing ovary make the experimental study of isolated follicular components very difficult.</p> <p>The recently developed laser capture microdissection (LCM) technique coupled with microarray experiments is a promising way to address the molecular profile of pure cell populations. However, one main challenge was to preserve the RNA quality during the isolation of single cells or groups of cells and also to obtain sufficient amounts of RNA.</p> <p>Using a new LCM method, we describe here the separate expression profiles of oocytes and follicular cells during the first stages of sheep folliculogenesis.</p> <p>Results</p> <p>We developed a new tissue fixation protocol ensuring efficient single cell capture and RNA integrity during the microdissection procedure. Enrichment in specific cell types was controlled by qRT-PCR analysis of known genes: six oocyte-specific genes (<it>SOHLH2</it>, <it>MAEL</it>, <it>MATER</it>, <it>VASA</it>, <it>GDF9</it>, <it>BMP15</it>) and three granulosa cell-specific genes (<it>KL</it>, <it>GATA4</it>, <it>AMH</it>).</p> <p>A global gene expression profile for each follicular compartment during early developmental stages was identified here for the first time, using a bovine Affymetrix chip. Most notably, the granulosa cell dataset is unique to date. The comparison of oocyte vs. follicular cell transcriptomes revealed 1050 transcripts specific to the granulosa cell and 759 specific to the oocyte.</p> <p>Functional analyses allowed the characterization of the three main cellular events involved in early folliculogenesis and confirmed the relevance and potential of LCM-derived RNA.</p> <p>Conclusions</p> <p>The ovary is a complex mixture of different cell types. Distinct cell populations need therefore to be analyzed for a better understanding of their potential interactions. LCM and microarray analysis allowed us to identify novel gene expression patterns in follicular cells at different stages and in oocyte populations.</p

Epigenetics and developmental programming of welfare and production traits in farm animals

The concept that postnatal health and development can be influenced by events that occur in utero originated from epidemiological studies in humans supported by numerous mechanistic (including epigenetic) studies in a variety of model species. Referred to as the ‘developmental origins of health and disease’ or ‘DOHaD’ hypothesis, the primary focus of large-animal studies until quite recently had been biomedical. Attention has since turned towards traits of commercial importance in farm animals. Herein we review the evidence that prenatal risk factors, including suboptimal parental nutrition, gestational stress, exposure to environmental chemicals and advanced breeding technologies, can determine traits such as postnatal growth, feed efficiency, milk yield, carcass composition, animal welfare and reproductive potential. We consider the role of epigenetic and cytoplasmic mechanisms of inheritance, and discuss implications for livestock production and future research endeavours. We conclude that although the concept is proven for several traits, issues relating to effect size, and hence commercial importance, remain. Studies have also invariably been conducted under controlled experimental conditions, frequently assessing single risk factors, thereby limiting their translational value for livestock production. We propose concerted international research efforts that consider multiple, concurrent stressors to better represent effects of contemporary animal production systems

106 GENOMIC IMPRINTING OF IGF2R IN TISSUES OF BOVINE FETUSES GENERATED BY ARTIFICIAL INSEMINATION OR IN VITRO FERTILIZATION

The insulin-like growth factor 2 receptor gene (IGF2R) is involved in fetal growth regulation. A study in sheep associated fetal overgrowth after in vitro embryo culture with abnormal DNA methylation and expression of IGF2R (Young et al. 2001 Nat. Genet. 27, 153–154). This suggested that abnormal IGF2R imprinting is a major cause of fetal overgrowth. To test this hypothesis in bovine fetuses, we developed a microsatellite marker for IGF2R from cDNA sequence data and screened 45 Day-80 fetuses generated in vivo, by artificial insemination (AI), or in vitro, by in vitro fertilization (IVF) procedures, for parent-of-origin-specific gene expression. A total of 17 fetuses were heterozygous, but available parental DNA samples showed that only 12 (8 AI, 4 IVF) allowed unambiguous discrimination of parental alleles. Parent-of-origin-specific allelic expression patterns indicated that bovine IGF2R was expressed predominantly from the maternal allele and thus imprinted in fetal heart, kidney, liver, lung, muscle, and cotyledon tissue. However, the relative amount of expression from the paternal allele was tissue-specific and ranged from 6.4 ± 0.8% in skeletal muscle up to 27.4 ± 0.9% in cotyledon (SPSS or 11.5, ANOVA, P < 0.001). Tissues that originated from the same germ layer showed similar allelic expression ratios whereas significantly different expression ratios (P < 0.05) were observed between tissues originating from different germ layers. Contrary to expectations from sheep data, there was no evidence for gross abnormalities in IGF2R imprinting in tissues from overgrown (n = 2) or normal sized (n = 2) IVF fetuses. However, relative paternal expression levels in several tissues showed significant relationships (P < 0.05–0.001) with growth parameters and pointed to subtle changes in paternal IGF2R expression in overgrown IVF fetuses. We thank W. Scholz and M. Weppert for excellent technical assistance